1. Field of the Invention
The present invention relates to an organic photosensitive material for electrophotography used for copying machines, laser printers and the like. More specifically, the invention relates to an organic photosensitive material for electrophotography containing a particular diphenoquinone derivative and having excellent sensitivity and residual potential.
2. Description of Prior Art
A source of light having a wavelength of longer than 700 nm is usually used for photosensitive materials for electrophotography that employs a digital optical system. As photosensitive materials that are sensitive in this wavelength region, there have been known organic photosensitive materials (OPCs), amorphous silicon (a-Si) and some selenium photosensitive materials. From the overall standpoint such as sensitivity and cost, however, OPCs are used in many cases.
Many organic photosensitive materials are those of the so-called function separated type, i.e., the laminated layer type in which a charge-generating layer (CGL) arid a charge-transporting layer (CTL) are laminated one upon the other. However, there have also been known organic photosensitive materials of the single layer type in which a charge-generating agent is dispersed in the medium of the charge-transporting agent.
The charge-transporting agents for the photosensitive material of this kind must have a high carrier mobility. However, the charge-transporting agents having high carrier mobility are in almost all cases are of the positive hole-transporting type. Therefore, those put into practical use are limited to those organic photosensitive materials of the negatively charged type. However, the organic photosensitive materials of the negatively charged type which utilize negatively charged corona discharge generate large amounts of ozone arousing such problems as polluting environment and deteriorating the photosensitive material. In order to prevent these problems, special systems are needed such as a particular electrifying system for preventing generation of ozone, a system for decomposing ozone that is formed, and a system for exhausting ozone in the apparatus, causing the process and the system to become complex. Moreover, the laminated layer type photosensitive material needs the photosensitive layer to be coated twice or the photosensitive layer has an interface that exists between the charge-generating layer and the charge-transporting layer and that develops interference fringes which is a problem from the optical point of view.
Among a few examples of the charge-transporting agents having electron-transporting ability, Japanese Laid-Open Patent Publication No. 206349/1989 proposes a compound having a diphenoquinone structure as a charge-transporting agent for electrophotography.
It has been said that the diphenoquinone derivatives exhibit good transporting ability but exhibit poor sensitivity when they are used for high-speed copying machines and are, hence, not yet satisfactory from the practical point of view.